flex-error: resolve conflicts with master

[thanethomson]

Follows from #923

• Referenced an issue explaining the need for the change
• Updated all relevant documentation in docs
• Updated all code comments where relevant
• Wrote tests
• Added entry in .changelog/

[codecov-commenter]

Codecov Report

Merging #945 (1efaa00) into soares/flex-error (2ea6da4) will increase coverage by 0.1%.
The diff coverage is 88.8%.

@@                 Coverage Diff                 @@
##           soares/flex-error    #945     +/-   ##
===================================================
+ Coverage               71.4%   71.6%   +0.1%     
===================================================
  Files                    201     203      +2     
  Lines                  16361   16480    +119     
===================================================
+ Hits                   11698   11811    +113     
- Misses                  4663    4669      +6     

Impacted Files	Coverage Δ
light-client/src/macros.rs	59.3% <ø> (ø)
light-client/src/store/memory.rs	66.6% <ø> (ø)
tendermint/src/chain/id.rs	71.6% <0.0%> (ø)
p2p/src/secret_connection.rs	88.8% <83.5%> (+0.4%)	⬆️
light-client/src/components/verifier.rs	100.0% <100.0%> (ø)
light-client/src/peer_list.rs	88.0% <100.0%> (ø)
light-client/src/predicates.rs	97.3% <100.0%> (ø)
light-client/src/supervisor.rs	89.2% <100.0%> (ø)
std-ext/src/lib.rs	100.0% <100.0%> (ø)
std-ext/src/try_clone.rs	100.0% <100.0%> (ø)
... and 13 more

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